1. Technical Field
This application is related to a method and apparatus for reducing injury/damage from collisions of a vehicle with other vehicles, obstacles, or pedestrians, and in particular, to such a method and apparatus that are operable based on a time factor called “a time to collision (TTC)”.
2. Related Art
Vehicle control units that perform vehicle control according to a probability of collision have been known. In such a vehicle control unit, a monitoring sensor, such as a radar or a camera, included in the vehicle control unit is used to sense an obstacle or a pedestrian (hereinafter collectively referred to as an “object”) located in a travel direction of the vehicle equipped with the unit (hereinafter also referred to as “the vehicle concerned” or just as “the vehicle” when comprehensible from the context). After an object is sensed, a time to collision (TTC) is calculated by dividing a relative distance between the object and the vehicle by a relative speed. Vehicle control according to a probability of collision between the object and the vehicle has been performed based on the TTC calculated as mentioned above.
As an example of such vehicle control units, collision injury/damage reduction apparatuses have been known. In such a collision injury/damage reduction apparatus, a probability of collision is determined to be high when the TTC becomes equal to a predetermined first threshold time TH1. When such a determination is made, an automatic braking system is forcibly operated irrespective of the driver's operation of the vehicle. Further, when the TTC becomes equal to a second threshold time TH2 (<TH1), a probability of collision is determined to be higher. In this case, protection devices provided at the vehicle are actuated to reduce injuries and damage that would be caused by the possible collision.
It sometimes happens that such a collision injury/damage reduction apparatus allows the protection devices to be actuated under the condition where there is no need of such an actuation (or allow a so-called erroneous actuation). In order to avoid such an erroneous actuation, it has been suggested that certain conditions of actuation be given and that the protection devices be actuated only when the conditions of actuation have been met. The conditions of actuation include, for example, that a relative speed used for the calculation of the TTC should be equal to or more than a threshold speed even when the TTC has become equal to the second threshold time TH2. Reference may be made, for example, to JP-A-2008-521691 for such a suggestion.
However, such a conventional collision injury/damage reduction apparatus makes a determination regarding whether or not the protection devices should finally be actuated, with reference to the relative speed prior to the time point of the determination. Meanwhile, the vehicle concerned may be decelerated by an automatic braking system to a level that the possible collision between an object, such as a pedestrian, and the vehicle would cause no injuries to the pedestrian or the vehicle occupants involved in the collision, or to a level of avoiding the collision. For this reason, it is very likely that the protection devices may be actuated when they are no longer needed to be actuated.
Specifically, for the sake of safety, it is required that a threshold speed be preset estimating a relative speed of collision between an object and the vehicle concerned. Meanwhile, it is difficult to change a preset threshold speed, for the purpose of reducing erroneous actuation of the protection devices. Therefore, a threshold-based determination (hereinafter referred to “threshold determination”) by merely comparing the relative speed before collision with the threshold speed, as has been conducted in the conventional art, will not reflect the change of the relative speed on or after the time point when the TTC becomes equal to the second threshold time TH2. As a result, the accuracy of a threshold determination tends to become comparatively low.